Issued on April 5, 1864, General Orders No. 15 from Headquarters, Army of the Potomac amended the organization of the provost-marshal’s department, the transportation allotments, and the organization of pioneer details. Paragraph II of the order dealt with the latter subject:
II. The following is established as the organization and equipment of the pioneer parties of this army:
First. The unit of organization will be by brigade. In each brigade 1 man shall be selected for every 50 men equipped for duty in it; for every 10 men thus selected a corporal shall be detailed, and for every 20 a sergeant, and for each brigade 1 lieutenant.
For each division a first lieutenant of old date or a captain shall be detailed to command the pioneers of the division, who will be a member of the division staff, and be furnished with a horse and equipments by the quartermaster’s department.
The pioneers will be armed as they were in their regiments, and men and officers will be especially selected for fitness for the duty. They will be excused from all guard and picket duty and from ordinary fatigue details. The tools will be furnished in the following proportions, viz, five-tenths axes, three-tenths shovels, two-tenths picks, and be carried on pack-mules during the march, each mule carrying the tools for 40 pioneers. The quartermaster’s department will provide the necessary mules and appropriate panniers for this service.
Brigade and division commanders are directed to give special attention to the prompt formation and equipment of their pioneer parties.
In camp, the pioneer parties will make the ordinary repairs to roads, build bridges, &c. On the march, they will move at the head of the infantry column and promptly put in order all parts of the route where artillery and wagons have to pass, whether for their own command or for troops to follow.
Second. Corps commanders will cause 1 non-commissioned officer and 25 efficient men to be selected and placed under the orders of the chief quartermaster of the corps to serve as a mounted pioneer party to accompany the trains, and to be provided with 10 axes, 10 spades, and 5 picks. The horses and equipments for the pioneers for the trains will be furnished by the quartermaster’s department.
The Army of the Potomac, and other field armies, used pioneer details throughout the war. This order established two “pools” of engineers – one supporting the maneuver elements and another for the corps trains.
And what was the mission assigned those pioneers? Building roads and bridges. There is a common interpretation that by 1864 tactical combat evolved into a entrenchment-dominated, semi-static infantry firefight. But, the shovel, pick, and axe were also tools to enable maneuver both to the battlefield and upon it. See, the Overland Campaign was far more than a series of frontal assaults and ever extending trench lines.
(Citation from OR, Series I, Volume 33, Serial 60, page 805.)